1. Field of the Invention
The present invention is directed to satellite transmit antenna analysis, design and optimization. More particularly, the present invention is directed to a system for and method of jointly optimizing two or more antenna patterns projected from respective satellites that use spatial diversity transmission techniques to minimize outages at ground-based receivers.
2. Background of the Invention
The Federal Communications Commission recently approved the use of selected radio spectrum for satellite radio broadcasting. Satellite radio broadcasting delivers up to 100 channels of audio to ground-based mobile receivers (radios) that may be installed in vehicles such as cars, boats, etc., and to traditional portable or non-portable radio receivers such as those embodied in stereo receivers or clock-radios.
One implementation for a broadcast segment of a satellite radio system comprises two geostationary satellites xe2x80x9cparkedxe2x80x9d at 85xc2x0 and 115xc2x0 West. In these orbits, virtually every location in the continental United States (CONUS) has a direct view of both satellites. In a preferred implementation of the broadcast segment, described in detail in U.S. Ser. No. 09/318,938, filed May 26, 1999, now U.S. Pat. No. 6,154,452 entitled xe2x80x9cMETHOD AND APPARATUS FOR CONTINUOUS CROSS-CHANNEL INTERLEAVING,xe2x80x9d and U.S. Ser. No. 09/433,861, filed Nov. 4, 1999, entitled xe2x80x9cMETHOD AND APPARATUS FOR CONCATENATED CONVOLUTIONAL ENCODING AND INTERLEAVING,xe2x80x9d now U.S. Pat. No. 6,229,824 (both of which are incorporated herein in their entireties by reference), two satellites employ diversity broadcasting techniques, which rely on interleaving signals on each satellite, as well as between satellites, so that in the event one satellite becomes blocked momentarily due, e.g., to terrain or buildings in an urban setting, the radio receiver can still decode the intended transmission and make the signal available for listening via speakers or headphones. Stated differently, the two cited references describe methods and apparatuses for implementing a satellite broadcasting system that uses spatial diversity techniques to minimize outages to radio receivers, and most specifically, to mobile radio receivers.
By having two satellites transmit different, yet related, signals that are both received and decoded (and thereafter combined in accordance with the aforementioned references) by a single radio receiver, the chances that the intended transmission is actually received and properly played for a listener are greatly increased. This is especially important for mobile radio receivers that may encounter frequent, yet relatively brief blockages. However, in order to fully exploit the advantages of employing two satellites that employ spatial diversity techniques to enhance the chances of receiving the intended transmissions, it is important to provide uniform high availability for each of the satellites.
It is therefore an object of the present invention to provide a system for and a method of optimizing the antenna patterns of at least two satellites to achieve a maximum combined availability across a predefined geographic region.
It is another object of the present invention to provide a system for and a method of calculating the most desirable antenna patterns for at least two satellites in a satellite broadcasting system that employs spatial diversity broadcasting techniques.
It is another object of the present invention to provide a system for and a method of determining the desired antenna patterns for at least two antennas, each on a separate geostationary satellite.
To achieve the foregoing and other objects, the present invention provides a system for and a method of jointly optimizing the transmit antenna patterns of two geostationary satellites in a satellite broadcasting system that uses spatial diversity techniques to minimize outages, especially to mobile receivers. While various techniques exist to combine signals from two or more satellites to minimize the periods of time when a signal is unavailable, none of these prior art techniques addresses a situation in which the antenna patterns of two geostationary satellites that employ spatial diversity broadcasting techniques might be adjusted to improve overall reception performance.
More specifically, when spatial diversity is employed, two geostationary satellites with a common coverage area provide redundant signal paths so that even though one path might be degraded, a high probability exists that the other path is less degraded. The present inventors recognized that in order to optimally design such spatial diversity systems it is desirable to manipulate the antenna patterns of the two satellites to provide uniform high availability without wasting power where it is not needed and without blindly using modeling techniques that result in physically impossible antenna configurations.
Thus, a process according to the present invention preferably involves initially determining a transmit power flux density (PFD) requirement for each individual satellite at a number of locations within a desired coverage area (e.g., CONUS) using an objective analytical model to determine the necessary margin to achieve a given availability. Then, in regions where one satellite""s antenna cannot achieve the desired power level just-calculated, the process involves reducing the requirement for that satellite and simultaneously increasing the PFD requirement for the other satellite in the same location, so that the combined availability for both satellites meets the desired level of availability.
Where it is impossible to meet the desired joint availability at all points or locations within the desired coverage area, the present invention calls for relaxing the PFD requirement for both satellites in areas with low populations and/or low intrinsic fading probability and re-allocating the xe2x80x9cfoundxe2x80x9d power to other terrestrial locations. The foregoing steps are repeated and the predicted joint availability is re-calculated until an acceptable antenna pattern solution is found.
The details and advantages of the present invention will become apparent upon a reading of the following detailed description in conjunction with the accompanying drawings.